As a planetary gear device, there has been proposed a two-stage planetary gear reduction device as shown in FIG. 6. The two-stage planetary gear reduction device 1 has a front-stage planetary gear mechanism 2 and a rear-stage planetary gear mechanism 3. The rear-stage planetary gear mechanism 3 has a circular internal gear 5, first and second carriers 8 and 9 which are rotatably supported by a pair of main bearings 6 and 7 disposed on both sides of internal teeth 4 on an inner circumferential surface of the internal gear 5, a plurality of planetary gears 11 engaged with the internal teeth 4 which are rotatably supported on a plurality of planetary shafts 10 extending between the first and second carriers 8,9 a sun gear 13 engaged with the planetary gears 11 which are formed on the outer circumference of a pinion shaft 12 extending through the carriers 8, 9 in a device axial line direction 1a, and an output shaft 14 connected to the second carrier 9 and extending in the device axial line direction 1a.
The front-stage planetary gear mechanism 2 has an internal teeth 15 formed on an inner circumferential surface of the first carrier 8 at the rear side, a plurality of planetary gears 16 engaged with the internal teeth 15, a carrier 17 rotatably supporting the planetary gears 16, and a sun gear 19 which is formed on the outer circumference of a pinion shaft 18 extending along the device axial line direction 1a and is engaged with the planetary gears 16. The carrier 17 is connected to the pinion shaft 12 at the rear side.
The planetary gear device as constituted above has the following problems that must be solved.
(1) In the rear-stage planetary gear mechanism 3, the first and second carriers 8 and 9 must be fastened with each other while the planetary gears 11 is held between them, and the output shaft 14 must also be fastened. With this structure wherein separate members are fastened, there are such problems that the manufacturing cost and assembly processes are increased, and assembly accuracy is degraded, as well as the number of component parts is large. PA0 (2) The pinion shaft 12 whose one end is connected to the carrier 17 at the front-stage side is rotatably supported at an outer circumferential surface portion of its axial end on an inner circumferential surface of the second carrier 9 via the main bearing. If the bearing portion of the pinion shaft 12 is made simplified in structure, it is advantageous in terms of its structure and manufacturing cost. PA0 (3) A bearing nut, shim, spring and other members are used to apply a pre-pressure to bearings such as the main bearings 6, 7 disposed to rotatably support the carriers 8, 9 on the inner circumferential surface of the internal gear 5. It is, however, that the bearing nut is expensive, the shim must be adjusted of its thickness, and the spring cannot be used where a sufficient space for its installation is not assured. Thus, it is desirable as the bearing pre-pressure mechanism that the manufacturing cost is low, workability is good, and it can be assembled in a narrow space. PA0 (4) It the main bearings 6 and 7 disposed to rotatably support the carriers 8, 9 on the inner circumferential surface of the internal gear 5 cannot be pre-pressured appropriately, when a bending moment is applied on the output shaft 14 and other portions as an external load, the span of bearing point of application between these main bearings becomes short, which gives rise to a fear that a large stress occurs. PA0 (5) In the front-stage planetary gear device 2, the planetary shaft 16a is mounted on the carrier 17 in a cantilevered condition, on which the planetary gear 16 is rotatably supported. In this case, a snap ring 16b is fixed on the end of the planetary shaft 16a to prevent the planetary gear 16 from removing therefrom. However, when the snap ring is used as a removal prevention mechanism, the end of the planetary shaft 16a must be worked to form a groove for the snap ring. There is also a possibility that the snap ring is attached in an imperfect manner. PA0 (6) The internal gear 5 is integrally formed on the device housing 5a. Such a structure is also known that the internal gear is manufactured separate from the device housing due to design and other aspects, and is assembled to the device housing, wherein fastening metallic parts such as a fastening screw are used to fasten the internal gear. This fastening method, however, requires time for tapping and increases manufacturing cost. PA0 (7) The planetary gear device is sometimes used as a gear head for a motor. For this reason, the planetary gear device is provided on its end surface with an adapter flange for use in motor mounting. The adapter flange is usually mounted to the side of the reduction device with fastening screws. If other component parts of the reduction device can be fastened with making use of the fixing force by the fastening screws, the structure of the reduction device can be simplified, the number of component parts can be reduced, and the manufacturing cost can be decreased. PA0 (8) As the planetary gear 10 or 16 rotates, the end surface thereof slides on the end surface of the carrier 8 or 9. In order to reduce sliding resistance between these parts, insertion of a washer or other means is adopted. However, attachment of such additional members causes to increase the number of component parts, and to make the assembly operation complicated since such members must be assembled.
An object of this invention is to provide a planetary gear device which is able to solve the above-mentioned problems.